The Twilight of Pluripotency?

Stem Cell Paradigms Shifting in 2018

Once hailed as the holy grail of regenerative medicine, embryonic and induced pluripotent stem cells faced mounting challenges—while tiny underdog cells called VSELs quietly stole the spotlight.

The State of the Stem Cell Field

When Stem Cell Reviews and Reports (SCRR) closed its 2018 volume, its impact factor had surged to 3.612—a testament to the journal's role in catalyzing critical discourse. Under Editor-in-Chief Mariusz Z. Ratajczak and a team of leading scientists, SCRR published nearly 80 articles that year, deliberately spotlighting controversial ideas alongside solid data 1 3 . Albert Einstein's warning—"A blind belief in authority is the worst enemy of truth"—anchored the journal's mission to interrogate stem cell orthodoxy 3 .

The central quest remained clear: identifying a clinically viable pluripotent stem cell capable of generating all three germ layers (ectoderm, mesoderm, endoderm). Yet 2018 revealed deepening fractures in the field's confidence in two former frontrunners:

  • Embryonic Stem Cells (ESCs): Ethically contentious and plagued by teratoma risk, immune rejection, and genomic instability
  • Induced Pluripotent Stem Cells (iPSCs): Though ethically simpler, they mirrored ESCs' risks and showed limited functional integration into damaged tissues—acting largely through paracrine effects 1 3 .
Table 1: Key Challenges for Pluripotent Stem Cells in 2018
Cell Type Advantages Critical Limitations Clinical Relevance
Embryonic Stem Cells (ESCs) Gold standard pluripotency Teratoma formation, immune rejection, ethical controversy Declining due to safety risks
Induced Pluripotent Stem Cells (iPSCs) Ethical, patient-specific Genomic instability, paracrine-only effects in trials Limited to disease modeling/drug screening
Very Small Embryonic-Like Stem Cells (VSELs) No teratoma risk, adult-tissue derived Difficult expansion ex vivo Emerging for tissue regeneration
ESC Research Decline
2018 Stem Cell Publications

VSELs: The Dark Horse Candidate

Amid skepticism toward ESCs/iPSCs, SCRR spotlighted Very Small Embryonic-Like stem cells (VSELs)—adult-derived cells expressing pluripotency markers but with distinct advantages:

  • No teratoma risk observed in transplantation studies
  • Primitive morphology enabling evasion of immune detection
  • Germline potential, as demonstrated by Irma Virant-Klun's work showing VSELs could generate oocyte-like structures responsive to sperm 1 4 .
VSEL Breakthrough

A breakthrough came from Philippe Henon's team, who achieved efficient ex vivo expansion of VSELs using UM177—a molecule modulating stem cell quiescence. This addressed a major roadblock: sourcing sufficient cells for therapy 1 3 .

Stem Cells SEM
VSEL Morphology

Scanning electron micrograph showing the small size and primitive morphology of VSELs compared to other stem cell types.

VSELs vs. iPSCs
  • Teratoma Risk VSELs: None iPSCs: High
  • Source VSELs: Adult tissue iPSCs: Reprogrammed
  • Ethical Concerns VSELs: Low iPSCs: Low

Decoding Pluripotency: CRISPR and mRNA Engineering

Two landmark 2018 studies exemplified SCRR's commitment to innovative solutions:

Jehuda et al. combined iPSCs with CRISPR/Cas9 to model inherited cardiac, neurodegenerative, and immune disorders 1 3 .

Table 2: Workflow for CRISPR-iPSC Disease Modeling
Step Procedure Purpose Key Outcome
1. iPSC Generation Skin fibroblast reprogramming Patient-specific pluripotent cells 0.002–0.08% efficiency
2. CRISPR Editing Cas9/sgRNA delivery to iPSCs Introduce disease mutations >70% editing efficiency
3. Differentiation Cardiomyocyte/neuron protocols Disease-relevant cell types Functional contractile/neural cells
4. Phenotyping Calcium imaging, electrophysiology Assess functional defects Identification of arrhythmia pathways

This pipeline revealed disease-specific phenotypes invisible in animal models—like metabolic stress-induced arrhythmias in cardiomyopathy-derived cardiomyocytes 3 .

Suknuntha et al. pioneered transgene-free iPSC generation using chemically modified mRNA. Traditional methods used viruses to deliver reprogramming genes (Oct4, Sox2, Klf4, c-Myc), risking genomic integration. Their approach 3 :

  1. Designed mRNA templates with pseudouridine and 5-methylcytidine to evade immune detection
  2. Achieved 0.02–1.2% reprogramming efficiency—surpassing plasmid-based methods
  3. Generated endothelial and hematopoietic cells at scales viable for drug screening 3 8 .
Table 3: mRNA vs. Viral Reprogramming of iPSCs
Parameter mRNA Method Viral Vector Method
Genomic Integration Risk None High
Efficiency 0.02–1.2% 0.001–0.1%
Time to iPSC Colonies 14–21 days 21–28 days
Clinical Applicability High (xeno-free versions available) Low
CRISPR-iPSC Applications
  • Disease modeling
  • Drug screening
  • Personalized medicine
  • Gene therapy development
mRNA Advantages
Safety (95%)
Efficiency (85%)
Scalability (75%)
Clinical Potential (90%)

The Scientist's Toolkit: Key 2018 Reagents

Critical advances relied on next-generation reagents, several commercialized for translational work:

Table 4: Essential Stem Cell Research Reagents in 2018
Reagent/Kit Function Application
Epi5 Episomal Reprogramming Kit Delivers Yamanaka factors + Lin28 via plasmids Viral-free iPSC generation (0.04–0.3% efficiency)
CytoTune-iPS 2.0 Sendai Kit RNA virus delivering Oct4/Sox2/Klf4/c-Myc High-efficiency integration-free iPSCs (0.02–1.2%)
UM177 Small molecule modulating CXCR4 signaling VSEL expansion ex vivo
Neon Transfection System Electroporation device Plasmid/mRNA delivery to stem cells
Epi5 Kit

Non-integrating plasmid system for safer iPSC generation

CytoTune 2.0

Sendai virus vector for high-efficiency reprogramming

UM177

Small molecule enabling VSEL expansion for clinical use

Beyond the Bench: Ethics and Evolution

SCRR's 2018 output underscored a philosophical shift: pluripotency alone is insufficient for clinical success. Safety, scalability, and functional integration became paramount. The journal actively curated debates on:

iPSC Twilight

Bhartiya's critique asked whether iPSCs merely provide "trophic support" instead of regenerating tissues 1

MicroRNA Regulation

Non-coding RNAs emerged as master switches for stem cell differentiation, offering new drug targets 3 5

VSEL Controversy

While promising, scalability hurdles remained, demanding better niche-mimicking cultures 1 .

"True innovation thrives not in the glare of certainty, but in the twilight of questioning."

Conclusion: A Field in Flux

The 2018 volume of Stem Cell Reviews and Reports captured a pivotal moment: the receding tide of iPSC/ESC euphoria and the rise of pragmatic alternatives like VSELs and precision-engineered iPSCs. As Ratajczak noted, the journal's commitment to "challenging and provocative ideas" mirrored the dynamism of a field questioning its core assumptions 3 .

This tension bore fruit—just months after SCRR's December issue, the first mRNA-reprogrammed iPSCs entered clinical validation, and VSEL-based reproductive studies advanced toward fertility restoration. In rewriting the rules of pluripotency, 2018 set the stage for a more biologically nuanced decade of regenerative medicine.

Key Takeaways
  • ESC/iPSC limitations became increasingly apparent in 2018
  • VSELs emerged as promising alternative with safety advantages
  • CRISPR and mRNA technologies revolutionized disease modeling
  • New reagents enabled more efficient and safer stem cell work
  • Field shifted focus from pluripotency to clinical practicality
2018 Milestones
January

First successful VSEL expansion with UM177

March

CRISPR-iPSC disease models published

June

mRNA reprogramming efficiency breakthrough

September

Ethical debates on iPSC limitations

December

SCRR impact factor reaches 3.612

Research Focus Areas
Further Reading

References